TRAPPIST-1 Planets Could Have Substantial Surface Water

The quest continues to learn more about the TRAPPIST-1 system, seven roughly Earth-sized planets orbiting a dwarf star about 39 light-years away. Whether life could exist on these planets is a matter of speculation at the moment, but scientists are honing in on measurements that could tell us if some of these alien worlds are habitable.

Advertisement - Continue Reading Below

The planets are rocky and some are the correct distance from their host star for liquid water, but they are probably tidally locked with the star, meaning the same hemisphere of the planet always faces the star, casting one half in perpetual daylight. In addition, they orbit much closer to TRAPPIST-1 than the planets of our solar system orbit the sun—in fact, the TRAPPIST-1 planets all orbit much closer to their host star than even Mercury to the sun. To make matters even more tenuous, stars like TRAPPIST-1, ultracool dwarf stars, are known to eject flares and supercharged particles at a high rate during their early years, possibly bombarding any planets with radiation and stripping away their atmospheres.

But there is some good news for those who hope our TRAPPIST-1 neighbors harbor life. A new study to be published in Astronomy & Astrophysics refined measurements for the mass and radius of the planets, and for the first time measured the amount of energy in the planets' interiors from tidal heating, which is energy generated by the gravitational tug of the star and other planets. The research suggest that two of the planets in particular, the third and fourth from the star, simply called TRAPPIST-1 d and e, have enough energy from tidal forces to sustain volcanic activity and significant amounts of water.

NASA/JPL-CALTECH

Advertisement - Continue Reading Below

"I think it's likely that planets d and e could have surface water in some places," Amy Mlinar, a planetary scientist with the Planetary Science Institute and lead author of the new study, told Popular Mechanics in an email. "Planet e is the most interesting to me, because its surface temperature is quite close to the melting point of ice—portions of the surface could be at just the right temperature for interesting ice tectonics and/or volcanism."

"Planet d has enough tidal heating to have a warm interior and potentially some volcanic eruptions on the surface of its rock layer," says Mlinar. "This, coupled with the warm surface temperature, leads us to believe that planet d could be habitable." The same goes for planet e, she says.

Another important calculation was made in the new study to estimate the extent of the greenhouse effect on the TRAPPIST-1 planets. A runaway greenhouse state could generate a thick atmosphere around the planets and heat the surfaces to conditions unfavorable to life, but the team found planets d and e were unlikely to be in runaway greenhouse states.

Advertisement - Continue Reading Below

Advertisement - Continue Reading Below

Planet c—the second closest to the star, as 'TRAPPIST-1 a' is the star itself—has also attracted interest among planetary scientists. The TRAPPIST-1 system is quite similar to the Jovian system of Jupiter and its moons. The planets, though much larger than Jupiter's moons, orbit at about the same distance to TRAPPIST-1 and at roughly the same rate. The Planetary Science Institute study suggests that planet c in particular could be similar to Jupiter's moon Io, with highly active volcanism at the surface and even permanently flowing surface lavas.

NASA/JPL-Caltech

Exactly what these planets are like is still unknown, and the likelihood that they are tidally locked results in a few possibilities. Without substantial atmospheres, the tidal locking would mean the light and dark halves of the planets would look very different, with possible water or volcanoes on the day side but likely cold ice and rock on the night side. With significant atmospheres, however, the planets could circulate much of their tidal energy to the dark side, and you would get a more uniform world with possible activity on both sides.

Advertisement - Continue Reading Below

We do not yet have a satisfactory answer regarding whether any of the TRAPPIST-1 planets have a significant atmosphere, however. A recent study suggested that some of the farther planets could have avoided the worst of TRAPPIST-1's radiation and clung on to their atmospheres, including planet e. But to find out for sure, astronomers will need more powerful telescopes.

Fortunately, a number are in the works. One of the primary missions of the James Webb Space Telescope, tentatively scheduled to launch next year, will be to study the atmospheres of exoplanets with its powerful infrared imaging capabilities. Ground-based observatories coming online in the 2020s will also focus on studying the atmospheres of exoplanets to look for signs of habitability, including the Giant Magellan Telescope and Extremely Large Telescope that will be constructed in the Atacama Desert of Chile, and the Thirty Meter Telescope that will sit on the Mauna Kea volcano of Hawaii.

Just 10 years ago, the abundance of exoplanets in the galaxy was assumed, but only a few hundred planets had actually been found. Now astronomers have discovered thousands, and many more are detected every year. Studying these mysterious worlds for signs of habitability has become one of the primary focuses of astronomy and planetary science, and the TRAPPIST-1 planets are close enough and similar enough to Earth that scientists won't rest until we know what dwells there, be it rocks, water, or organisms.

A Part of Hearst Digital Media
Popular Mechanics participates in various affiliate marketing programs, which means we may get paid commissions on editorially chosen products purchased through our links to retailer sites.